106 Croupous Pneumonia. 



Susceptibility. On account of the great prevalence of 

 influenza, horses are most connnonly affected with croupous 

 pneumonia, as far as domestic animals are concerned. It is 

 not merely relatively but absolutely frequent among horses and 

 follows in frequency the colicky diseases. Younger, well 

 nourished horses are most commonly alfected; poorly nourished 

 and overworked horses are less susceptible ; young foals still 

 less. Other domestic animals are affected more rarely or not at 

 all by this form of pneumonia. 



Anatomical Changes. Croupous pneumonia begins with an 

 active hyperemia in a large continuous usuallj^ lower or anterior 

 portion of one or both lungs (stadium hyperaemiae). The 

 parts which are situated near the root of the lungs (pulmonia 

 centralis) or the posterior, or still more rarely the upper por- 

 tions are not often affected alone. Simultaneously with 

 hyperemia there appear, not uncommonly, smaller or larger 

 hemorrhagic foci. Extravasation of blood serum with white 

 and red blood corpuscles occurs from the vessels into the alveoli 

 and into the finest bronchioles, where the exudate coagulates 

 at once, so that the affected pulmonary tissue becomes similar 

 in consistency to hepatic tissue (stadium hepatisationis). The 

 affected lung portion appears enlarged at this stage ; its tissue 

 is peculiarly tough and friable and it sinks in water. The cut 

 surface, particularly on oblique illumination, appears uniformly 

 finely granular and not juicy. Its color is at first red or brown- 

 red (st. hepatisationis rubrae) ; afterward, however, fibrin and 

 white corpuscles predominate in the exudate over the red blood 

 corpuscles, the cut surface assumes a reddish-gray (st. hepatisa- 

 tionis griseo-rubrae), and later on a light gray color (st. 

 hepatisationis griseae). Still later a yellowish color becomes 

 more prominent in consequence of fatty degeneration (st. 

 hepatisationis flavae). 



While the inflammation sets in simultaneously in larger t-ections of the 

 lungs, there are some deviations in the ai)pearance of the cut surface; hence 

 it frequently appears mottled (like granite), and red, gray and yellowish spots 

 and streaks are found side by side. This so-called marbled appearance is also seen 

 in croupous inflammation of cattle. However, the interstitial bands, if widened 

 at all, are often only gelatinous, dilated lymph clefts not being visible, and the 

 ground substance of the hepatized ])ortions is much alike in color (see Vol. I). 



After the exudate has become liquefied a reddish thick 

 fluid mixed with fine air bubbles and fat droplets may be scraped 

 off the cut surface, the consistency of the tissue has become 

 softer. This stage of resolution leads to recovery after absorp- 

 tion and expectoration. 



Tn the alveoli of the hepatized pulmonary tissue a reticulum may be seen 

 under the microscope formed of fine threads of fibrin ; its meshes are filled with 

 white and red blood corjtuscles, desquamated epithelia and granular detritus. Later 

 on the alveoli contain only detritus and fat granules. The interstitial connective 

 tissue shows an inflammatory infiltration with round cells and the fibers of the septa 

 li;i\(' IiecM |iiisli('(l ajiart by an odeniatnus infiltration. 



